LPG: The product

LPG - A Global Fuel

Worldwide LPG demand has grown by more than five per cent a year during the last decade. Currently, demand is around 220 million metric tonnes/year.

LPG is a global fuel. Although the majority of production is in North America and the Middle East, it is used in most countries of the world. Demand has been growing strongly in Central America, the Middle East and Asia although some African countries have also experienced particularly high growth rates. It is estimated that half the global LPG demand will arise in developing countries within 30 years.

Nearly fifty percent of the world’s LPG demand is in the domestic and commercial markets where it is used for cooking, space heating and water heating. It is becoming increasingly popular as an automotive fuel.

The impact of this growth on society and the environment is significant as LPG is displacing solid fuels such as coal, wood, charcoal and cow dung. These traditional fuels produce dust, dirt and smoke, which may cause severe health problems. As a result LPG is making a significant contribution in improving air quality levels in the home, in commercial kitchens and in restaurants.

The use of LPG as an automotive fuel has led to significant improvements in street level air quality by displacing traditional automotive fuels such as diesel and gasoline. Automotive LPG offers considerable strategic and environmental benefits in the supply and economics of automotive fuel.

There are other social issues associated with this changing domestic fuel use. No longer does the household have to deal with the messy collection and storage of solid fuel, and prepare and clean appliances. LPG further eliminates the risk of burns from lingering fires.

Properties of LPG

LPG, or Liquefied Petroleum Gas, is the term widely used to describe a family of light hydrocarbons. The two most prominent members of this family are propane (C3H8) and butane (C4H10). LPG is derived from natural gas processing and crude oil refining.

Natural gas may contain up to 10% propane and butane, which has to be extracted out before it can be transported. LPG represents about 3% – 10% of typical crude oil refinery production. The refinery is designed to mainly produce other fuels such as diesel, gasoline, heating oil and kerosene.

LPG is lighter than water as a liquid but heavier than air as a gas. In their liquid state propane and butane have the appearance of water but with have only about half the density

In vapour state, LPG is heavier than air and tends to settle down

Typical Properties of LPG
Chemical Formula C3H8 C4H10
Boiling point at 101.3 kPa (°C) -42.1 -0.5
Liquid density at 15 °C (kg/m3) 506.0 583.0
Absolute vapour pressure at 40 °C (kPa) 1510 375
Flash Point (°C) -104 -60
Upper flammable limit (% vol. in air) 9.5 8.5
Lower flammable limit (% vol. in air) 2.3 1.9
Vol. vapour per vol. liquid 269 235
Relative vapour density (air = 1) 1.55 2.07
Coefficient of expansion (liquid) per 1°C 0.0032 0.0023
Minimum air for combustion (m3/m3) 24 30
Kinematic Viscosity (centistokes) @ 20°C 0.20 0.30
Latent Heat of Vapourisation (kJ/kg) @ 20°C 352 368
Specific Heat (kJ/kg/°C) @ 20°C - liquid 2.554 2. 361
Specific Heat (kJ/kg/°C) @ 20°C - vapour 1.047 1. 495
Minimum ignition temperature (°C ) in oxygen 470 - 575 380 – 550
Maximum Flame temperature (°C ) 1980 1990
Octane number >100 92
Specific Energy (gross) kJ/kg 49.83 49.40

Propane and butane boil at different temperatures - propane at around – 42°C, butane at around 0°C. The gas produced when propane and butane boil (vaporise) is invisible and has no natural odour (although a disagreeable unpleasant odourant is added to aid the detection of a leak). A liquid leak will give the appearance of a white cloud (see photo above which illustrates this under controlled release conditions)

In liquid form the volume of LPG changes significantly in response to changes in temperature. As a result storage containers are never filled to capacity to allow expansion to take place without causing an uncontrolled release of gas or damage to the container.

LPG is easily stored as a liquid under moderate pressure. One unit of liquid expands to about 250 units of vapour.

The flammable range is a mixture of between 2 and 10 % LPG in air. This mixture needs around 24 times (for propane) and 30 times (for butane) the same volume of air for complete combustion which means LPG needs adequate ventilation for burning. The energy content is very high and it produces a very hot flame. For more details on the properties of LPG refer to Guidelines for Good Safety Practice in the LPG Industry.

Product Benefits

The physical properties of LPG enable significant amounts of energy to be transported easily as a liquid under moderate pressure, yet when used it has the attributes of a gas. Because LPG consists of mixtures of propane and butane, specifications have been established for many different applications. For more information on this important subject see Guidelines for Good Safety Practice in the LPG Industry.

LPG is a clean burning fuel. This allows it to be used in direct contact with food (e.g. ovens) and articles such as fine pottery.

LPG has environmental and health benefits. It is non-toxic and will not contaminate aquifers or soil. If spilt, LPG will evaporate and disperse into the atmosphere. Unlike methane, the constituents of LPG (Propane and Butane) do not contribute to the atmospheric greenhouse gas loading

Main Applications

LPG can power the smallest domestic appliance or the largest industrial application. In addition to its many applications as a fuel, LPG is also an important feedstock for the chemical and plastics industry.

Clean burning LPG is ideally suited for domestic and commercial cooking, space heating and water heating, and power generation, particularly in remote locations.

LPG assists farmers to increase their output, and improve the quality, of crop production through weed flaming, crop harvesting, and crop drying. LPG is also used to heat breeding houses for pigs and poultry, and powers farm equipment such as irrigation pump engines.

There are almost no limitations for LPG use in the industrial sector. Some common applications include heat treatment furnaces, direct firing of ceramic kilns, glass working, textile and paper processing, paint drying and cotton singeing, process heat (oil and steam) and forklift fuel.

The purity of LPG also enables it to be used as an aerosol propellant in unodourised form.

The clean burning nature and portability of LPG has led it to become one of the fastest growing transport fuels. Although it has been used for years as a low emission alternative to gasoline and diesel forklift trucks, recently LPG is being used more for on-road applications such as taxis, private cars and buses. The photo opposite is an example of a LPG fueled vehicle.

Finally, the versatility of LPG allows users to rationalise on one form of energy eliminating the need for storing and handling several different types of fuel.

LPG is a popular alternative automotive fuel in many markets across the world